Such a disk drive device has recently required miniaturization, thinness, high performance, a low cost, and the like. In addition, when the disk drive device is used on a vehicle, it has required clamping reliability, vibration resistance, shock resistance, and dust resistance. In connection with this, a disk clamping mechanism becomes more important to stably hold the disk such that a disk rotating motor that supports and rotates an optical medium meets the above-described requirements.
A clamping mechanism that holds the disk in a turntable unit under pressure by the force of a spring disposed in a damper mounting mechanism was mainstream in a vehicle-mounted use of the disk clamping mechanism. However, a disk clamping mechanism by the use of a magnet attractive force that can secure a high disk holding force has been mainstream because the accuracy of equipment becomes high according to a recent increase in recording capacity (see, for example, Patent Document 1).
FIG. 2 shows a disk rotating motor and a disk clamping mechanism in the related art disclosed in Patent Document 1.
As shown in FIG. 2, the conventional disk clamping mechanism is provided with a centering member 103, a clamping magnet 104, and a back yoke 105. Centering member 103 is adapted to hold an inner diameter portion 102 of a disk 101. Clamping magnet 104 is contained in centering member 103. Back yoke 105 is disposed so as to secure a magnetic flux of clamping magnet 104. The disk clamping mechanism is fixed at the center of a turntable unit 107 having a rubber sheet 106, serving as a disk mounting surface, stuck thereto. A damper 109 containing a magnet 108 therein and rubber sheet 106 hold disk 101, thereby achieving stable holding.
As for clamping a back yoke in the disk clamping mechanism, there has been further conventionally proposed the following techniques. For example, a back yoke 110 is molded integrally with a centering member 111 in a disk rotating motor in the related art shown in FIG. 3 (see, for example, Patent Document 2). A back yoke 112 is securely press-fitted into a shaft 113 in a disk rotating motor in the related art shown in FIG. 4 (see, for example, Patent Document 3). A back yoke 114 is incorporated and fitted via an engaging portion 115 formed in a centering member in a disk clamping structure in the related art shown in FIG. 5 (see, for example, Patent Document 4).
Moreover, apart from the above-described related art, there has been proposed a structure, in which a magnet is directly mounted on a turntable unit, and further, the turntable unit is used also as a back yoke (see, for example, Patent Document 5).
FIG. 6 shows a disk rotating motor and a disk clamping mechanism disclosed in the related art in Patent Document 5.
As shown in FIG. 6, a magnet 117 is constituted integrally with a disk 116. In the meantime, a clamping magnet 119 is mounted directly on a metallic turntable unit 118. Disk 116 is configured to be securely pressed against a side wall 120 of turntable unit 118 by the attractive force of magnet 117 and clamping magnet 119. In this manner, turntable unit 118 serves also as a back yoke.
However, with the configuration disclosed in Patent Document 1, a method for fixing the magnet and the back yoke is not obvious. Assuming fixing via bonding, clamping reliability and shock resistance are poor in severe use environment during a vehicle-mounted use. Additionally, the upper plane of the magnet is exposed, and therefore, a magnetic member may possibly attract minute foreign matters, thereby making it difficult to secure dust resistance.
With the configuration disclosed in Patent Document 2, the back yoke is molded integrally with the centering member, thus achieving high clamping reliability and high shock resistance. However, integral molding is relatively expensive in the market that requires a lower cost, and therefore, the configuration is disadvantageous from the viewpoint of a cost. In addition, in the case where a temperature shock peculiar to a vehicle-mounted use is applied in a wide range, an excessive stress is concentrated on the centering member due to a difference in thermal expansion coefficient between the materials of the centering member and the back yoke, thereby raising a possibility of occurrence of a crack.
With the configuration disclosed in Patent Document 3, the back yoke is press-fitted and clamped to a rotary shaft, and therefore, clamping reliability and shock resistance are high. However, the back yoke requires a constant or greater thickness in order to secure press-fitting strength. This has no other choice but to be a disadvantageous structure for the disk rotating motor requiring miniaturization and thinness.
With the configuration disclosed in Patent Document 4, the back yoke is securely engaged, and therefore, clamping reliability and shock resistance are high. However, its structure becomes complicated, so that not only component parts require high precision but also man-hours needed to assembly are increased. As a consequence, it is disadvantageous from the viewpoint of a cost.
With the configurations disclosed in Patent Document 2 to 4 in the same manner as the configuration disclosed in Patent Document 1, the upper plane of the magnet is exposed, and therefore, the magnetic member may attract minute foreign matters, thereby making it difficult to secure dust resistance.
Furthermore, with the configuration disclosed in Patent Document 5, since the magnet is mounted directly on the turntable unit, it is free from a problem to be solved of clamping the back yoke, and further, a member dedicated to the back yoke is unnecessary. Consequently, the number of component parts can be reduced, and therefore, it is advantageous from the viewpoint of a cost. However, in the same manner as the configurations disclosed in Patent Document 1 to 4, the degradation of dust resistance could not be overcome.